Heretofore, there have been known thermionic converters such as those shown in U.S. Pat. Nos. 3,519,854, 3,328,611, 4,303,845 and 4,323,808 (all to the inventor of the present invention), which disclose various apparatus and methods for the direct conversion of thermal energy to electrical energy. In U.S. Pat. No. 3,519,854, there is described a converter using Hall effect techniques as the output current collection means. The '854 patent teaches use of a stream of electrons boiled off of an emissive cathode surface as the source of electrons. The electrons are accelerated toward an anode positioned beyond the Hall effect transducer. The anode of the '854 patent is a simple charged metallic plate.
U.S. Pat. No. 3,328,611 discloses a spherically configured thermionic converter, wherein a spherical emissive cathode is supplied with heat, thereby emitting electrons to a concentrically positioned, spherical anode under the influence of a control member and having a high positive potential thereon. As with the '854 patent, the anode of the '611 patent is simply a charged metallic surface.
U.S. Pat. No. 4,303,845 discloses a thermionic converter wherein the electron stream from the cathode passes through an air core induction coil located within a transverse magnetic field, thereby generating an EMF in the induction coil by interaction of the electron stream with the transverse magnetic field. The anode of the '845 patent also comprises a charged metallic plate.
U.S. Pat. No. 4,323,808 discloses a laser-excited thermionic converter that is very similar to the thermionic converter disclosed in the '845 patent. The main difference is that the '808 patent discloses using a laser which is applied to a grid on which electrons are collected at the same time the potential to the grid is removed, thereby creating electron boluses that are accelerated toward the anode through an air core induction coil located within a transverse magnetic field. The anode of the '808 patent is the same as that disclosed in the '845 patent, i.e., simply a charged metallic plate.
It has been found that using a metallic plate as the anode has several associated disadvantages. These disadvantages include unwanted electron scatter occurring when the electron beam or bolus contacted the anode. Electron scatter acts to neutralize the static charge built up on the charged member, thereby reducing the acceleration and amount of electrons attracted to the anode. Thus, electron scatter can act to eventually cause the anode to cease attracting electrons, thereby destroying the function of the anode and rendering the converter inoperable.